Data communications is important to an ever increasing number of applications, both personal and business oriented. As the data itself becomes more critical and as the need to communicate that data increases, transmission speed becomes the focus of concern. Increasing the transmission speed, however, is not a straightforward process. As data is transmitted across the communications medium, i.e., telephone wire, cable, etc., the data signal is distorted. This distortion is generally in the form of noise and intersymbol interference. As more distortion is introduced, extracting the transmitted signal from the received signal becomes a more complicated process.
A common method used in extracting transmitted signals from received signals includes the use of an equalizer which includes an adaptive filter. Using adaptive equalization techniques, time varying characteristics of the transmitted signal are used to eliminate amplitude and phase distortion introduced by the communication channel. These distortion effects, however, extend beyond the time interval used to represent the data. Furthermore, as the need for faster and faster data communication increases, the need for a method and system which can retrieve a transmitted signal from the received signal with as little delay as possible increases.
One such system is shown in FIG. 1. The system includes a transversal filter 10 which accepts as input sampled data signals x(n), where n represents the sequence number of the data sample. The transversal filter 12 generates filtered output data, y(n), which is processed by a zero memory, non-linear estimator 12 to generate digitized output symbols y(n). An error signal, e(n), is determined at summation 14 by subtracting the filtered output data, y(n), from the digitized output symbols, y(n). An LMS processor 18 uses the error signal, e(n), to generate weights used to adjust the transversal filter 10 to the communications channel to reduce the error signal, e(n).
Intersymbol interference, one form of channel distortion, is caused by limited bandwidth in the channel. Sampling at a finite rate is another contributing factor. In retrieving the transmitted signal from the received signal typically oversampling with an equalizer is used to help minimize intersymbol interference. However, the equalizer which runs at the oversampling rate is much more complex and requires more calculations to accomplish the task.
Thus, what is needed is a efficient method and system for controlling an equalizer which reduces intersymbol interference when oversampling a transmitted data signal.